1. Field
The present disclosure relates to a recombinant bacterial strain extracellularly secreting fatty acids by using phospholipase activity and a method of producing fatty acids by using the same.
2. Description of the Related Art
Modern industries have still heavily depended on fossil fuels for use as source materials for chemical industries and as energy sources. The use of fossil fuels causes economic problems, including an increase in costs due to limited fossil deposits, and various environmental problems, including an increase in the concentration of carbon dioxide in air. The claim that future technology to brace for various environmental problems caused by the use of fossil fuels and depletion of fossil is needed still gains attention with social awareness. However, until now, new renewable energy having sustainability and economic competitiveness, which can replace the existing fossil fuels, has not been developed.
Recently, as a way to develop new renewable energy, the research to produce fatty acids either by fixing carbon dioxide or by reusing waste organic materials is being carried out. Fatty acids are converted into fatty acid ester through available chemical reactions, and fatty acids and derivatives thereof can be used as new renewable energy that replaces the oil from fossil fuel. Accordingly, in view of economic competitiveness due to an improvement of fatty acid producing technology and socio-politics, the practical use of fatty acids and derivatives thereof as an alternative energy source may be realized sooner than expected.
Unsaturated fatty acids are high value-added materials due to their use as a source material for medical products, cosmetic products, animal feeds, and heath supplements, as well as energy sources. In the past, only fatty acids with pre-determined composition could be produced by using, for example, plants and microalgae. However, technical advances in synthetic biotechnology, allow the composition of a fatty acid to be changed according to a desired purpose, and in particular, now, it is possible to increase the amount of useful unsaturated fatty acids to substantial levels.
The first-generation fatty acid production method uses neutral fat-rich plants to obtain fatty acids. However, this method requires a big land that could be used for crop culture otherwise, and accordingly, in consideration of global environmental change and imbalanced food production, the first-generation method is likely to face ethical problems. In this regard, in the future, the development of the fatty acid production by this method needs to be focused on use of places such as desert, mountainous regions, or the sea.
Microalgae are able to store lipid in large quantity per cell. However, up until now, it is difficult to readily apply the genetic methods thereto, and accordingly, additional increase of fatty acid productivity may not be feasible by using metabolic engineering methods. In addition, in the case of typical processes of producing fatty acids from plants and microalgae, processes for the pre-treatments of cells and the extractions of fatty acids are expensive and cause secondary contamination.
Korean Publication Patent No. 10-2009-0068266 provides information about polypeptides having phospholipase activity, nucleic acids coding for the polypeptides, and antibodies binding to the phospholipase. This publication provides an industrial method of degumming oil from a composition containing phospholipase. Korean Publication Patent No. 10-2011-0034116 provides a method of producing phospholipid, of which composition is changed by substituting a fatty acid of phospholipid by using immobilized phospholipase. The present disclosure is similar to these two publications in terms of the use of phospholipase as an active ingredient. However, the present disclosure, unlike these publications, uses phospholipase to secrete more fatty acids from bacterial cell that was genetically modified to synthesize more fatty acids.
The fact that fatty acids are extracellularly secreted by the action of thioesterase has been well known in many publications including Lennen and Pfleger (2012. Cell. 30: 659-667.). Like the present disclosure, US Publication Patent No. 2012/0237987A1 also discloses the secretion of fatty acids out of cyanobacterial cell. However, this publication is different from the present disclosure in that thioesterase, which is an enzyme using an acyl-acyl carrier protein (acyl-ACP) as a substrate, is used to induce the secretion of fatty acids. In addition, the present disclosure is different from the existing invention in that instead of expression of thioesterase in cytoplasm, phospholipase is expressed in a periplasmic space between an inner membrane and an outer membrane to efficiently decompose membrane phospholipids to form free fatty acids, which are then easily secreted out of the bacterial cell.
The above-mentioned background is presented herein only to help understanding of the background of the present disclosure, and shall not be considered to one of ordinary skill in the art as approving that the presented background is the prior art.